Transmissions, particularly, multistage transmissions including a plurality of pairs of transmission gears, installed in vehicles, employ the following configuration. Specifically, a speed change operation is performed with a sleeve, mounted on a main shaft and a counter shaft to be slidable in an axial direction, driven by a shift fork to fit with the transmission gear. For example, Patent document 1 discloses a dog clutch mechanism achieving the fitting between the sleeve and the transmission gear, through fitting between dog teeth provided to the sleeve and dog holes provided to the transmission gear. The dog clutch mechanism may further include a synchromesh mechanism to be a synchromesh-dog clutch mechanism. The dog clutch mechanism is provided in a manual transmission with the sleeve, for switching the speed change stage, manually slid. The dog clutch mechanism is also provided in an automatic transmission including an actuator mechanism that makes the sleeve automatically slide with a hydraulic actuator.
The dog clutch mechanism described above might involve contact between distal ends of the dog teeth of the sleeve, slid toward the transmission gear, and distal ends of the dog teeth of the transmission gear, leading to insufficient meshing between the dog teeth, resulting in engagement failure of the dog clutch mechanism. In this case, the engaging operation needs to be reattempted with the sleeve retracted. Thus, the manual transmission involves potential cumbersomeness that the speed change operation may need to be repeatedly attempted. In the same situation, the automatic transmission including the actuator mechanism described above reattempts (retries) the speed change operation after a detection means such as a sensor detects the engagement failure of the dog clutch mechanism. As a result, the speed change operation is delayed or hindered in other ways, and thus might not be smoothly conducted. All things considered, a driver of a vehicle including the transmission might feel irritated through a driving operation.
The contact between the dog teeth might result in small broken pieces breaking off from the dog teeth. The small broken pieces might be caught in hydraulic equipment such as a valve mechanism and a pump of the transmission, to disable the normal operation of these components. Furthermore, the small broken pieces might also be caught in a bearing, rendering a service life of the bearing shorter.
The conventional dog clutch mechanisms have been unable to completely eliminate the risk of the shifting failure due to the contact between the distal ends of the dog teeth. Thus, the transmission including the conventional dog clutch mechanism requires the speed change operation to be reattempted when the engagement failure of the dog clutch mechanism occurs.
Patent document 1 discloses a technique of detecting a meshed state of a dog clutch based on a difference between inner and outer main shafts in rotational speed, and an output signal from the gear position sensor. This configuration can accurately detect the engagement failure of the dog clutch, for reattempting the engaging operation (speed change operation). However, this does not offer a solution that can eliminate the need for reattempting the engaging operation of the dog clutch that hinders the smooth speed change operation.
Patent document 2 discloses a configuration for overcoming the task of the dog clutch for twin clutch transmission, that is, the failure to achieve the smooth fitting due to the contact between the distal ends of the dog teeth. Specifically, hydraulic control is employed to guarantee the fitting of the dog clutch for first speed and second speed. However, the conventional technology described in Patent Document 2 requires a hydraulic actuation device that needs control involving complexity and a certain amount of time.
As described above, various configurations for overcoming the disadvantages related to the contact between the dog teeth in the dog clutch mechanism have been proposed. Still, further technical improvement is expected to achieve a simple and inexpensive configuration ensuring a successful engaging operation of the dog clutch mechanism regardless of the relative rotational positions of the sleeve (slide member) and the gear (rotation member).